It just seems hard when you start cause of all the differant rtv. Lets make it simple use a rtv that is 25 to 30 in shore hardness. It will work for your needs now. If you want a two piece mold use a 30. If you want to use the one piece mold method use a 25 ,this is more flexible and easier to get the piece out of the mold. I do not need to see through my one piece mold to cut them open cause I use two dowels for my pour spouts and index my cuts from there. I split it with a razor till i can get my master out. When i close it up again it goes back to an almost seamless split. As for degassing that is dependant on the time you have to work the rtv after it is mixed. If it is a short time degassing ia a waste of time, it is just to hard to pour when it starts to set up. And I do use a food saver to pull my vacumn. My best friend is pressure to the tune of 30 psi. Now I know you are thinking BIG BUCKS,no harbor freight has a pressure pot for paintingthat will work with a few plumbing fittings. If you cant get pressure do your self a favor and try this,Before you pour in the box put a coat of rtv on your master especially on the bottom. Them pour from a height so air cannot be transfered in your pour. The reason for this is that bubbles will rise from the bottom and get trapped under the bait and you will end up with bubbles on that side forever. With the coat of rtv the chances will deminish drasticly. I have so called wasted some rtv in my time and this advice comes from experiance. To make it even easier try tap plastics blue rtv it is easy to use and without any other choice it is easy to pick the right one. I use this one cause there is a store close. One thing i would watch out for is schringage, this not your friend. This comes from fillers and not good for what you are doing. As for quantity I have always bought it by weight not volume so I do not know what a gallon looks like. This goes for resins to, fillers are not good and if they say it is the some but cheaper it has some type of filler to make up the differance. Hope this does not make things worse. Frank